This invention relates to airless paint sprayers, and more particularly, to a mechanism for providing a high flow rate of paint spray in a paint sprayer.
In a typical airless paint sprayer, a piston driven diaphragm pulls the paint from a supply line past a check valve into a paint holding or diaphragm chamber. On piston reversal, the paint in the diaphragm chamber is pressurized. A spray gun has a trigger which, when depressed, opens a valve to allow the pressurized paint in the chamber to flow through an outlet check valve and through a gun nozzle to atomize the paint as it exits an orifice for spraying onto a surface to be coated.
Airless paint sprayers commonly include a suction tube inserted within a can of paint through which the paint is delivered to the diaphragm chamber. Suction is created in the suction tube by a deformable diaphragm which is secured around its perimeter. A central portion of the diaphragm is oscillated, by a piston-driven hydraulic system, for example, between a convex and a concave configuration to thereby pull the paint toward the diaphragm and hence force it outwardly to the spray gun.
In another format, a rotating eccentric cam drives a bearing which in turn drives a piston. The piston is coupled to the diaphragm and the rotation of the cam drives the piston to thereby move the diaphragm to and between the convex and concave configurations. The paint is drawn from the can through the suction tube and inlet valve toward the diaphragm and into the diaphragm chamber to be discharged through the outlet check valve to the spray gun.
Despite past efforts, the use of such systems for spraying paint, for example, have been subject to inconsistent results and unexplained, undesirable variations. For example, a system may not work well with one paint, failing to fully atomize it and "spattering" it onto a surface while operating efficiently with the same paint at another time or in another location. Solutions to these types of problems have been identified as shown in two related applications for U.S. patent Ser. Nos. 08/370,159, filed Jan. 9, 1995 and 08/370,377, filed Jan. 9, 1995, each of which are assigned to the assignee of this invention and are expressly incorporated herein by reference. The inventions of those applications solve certain problems of poor paint sprayer performance.
Other problems which are commonly identified in airless paint sprayers include inconsistent spraying, for example, ineffective spraying of paint of a first type but efficient spraying of paint of a second type. Several possible causes of problems of this type have been proposed such as lack of consistent priming, paint buildup, clogged filters, paint viscosity variation resulting in flow rate variations, humidity, etc. Specifically, a lower flow rate of the paint through the sprayer occurs when a higher viscosity paint is sprayed even when the filters are clean and the flow path of the paint is unclogged. Paint viscosities typically range from about 3.8.times.10.sup.-4 ft.sup.2 /sec to about 1.5.times.10.sup.-2 ft.sup.2 /sec. The viscosity of water is even less, about 1.07.times.10.sup.-5 ft.sup.2 /sec. The inventions of applications Ser. Nos. 08/370,159 and 08/370,377 improve the performance of airless paint sprayers, but the variations in flow rate of higher viscosity paints and fluids as compared to lower viscosity paints and fluids prevent uniform performance. For example, flow rates of higher viscosity paints can be about 25% lower than the flow rate for less viscous paints and fluids.
Accordingly, the effective and consistent use of an airless paint system appears to be a sometimes thing dependent on flow rates resulting from the viscosity of the specific paint or fluid used in the system.
Therefore, it is apparent that there is a need for an airless paint sprayer which does not exhibit significant flow rate variations or loss of pressure, while spraying, due to the viscosity variations of fluids pumped and can reliably, efficiently and effectively spray all types of paint having a wide range of parameters, including viscosity, without the above identified problems and inconsistencies.
While the lower viscosity paints and fluids are relatively easy to handle and consistently pump at desired flow rates, use of the same valving and pumping structures for higher viscosity fluids runs into problems as a result of the more viscous fluids. The same pump and valve structure which works well with lower viscosity fluids does not work well with the higher viscosity fluids in the anticipated viscosity ranges of all paints intended for spraying.
It has thus been one objective of the invention to provide an improved airless sprayer capable of producing consistent spraying results for all anticipated paint viscosities.
It has been another objective of this invention to provide an improved airless paint sprayer which has a consistently high flow rate and does not loose pressure while spraying.
It has been a further objective of this invention to provide such a paint sprayer which can be efficiently and effectively used with a variety of paint types without loosing flow rate or pressure while spraying regardless of normally anticipated variations in paint viscosities.
It has been a still further objective of this invention to provide such a paint sprayer which can be used with a variety of paints and fluid viscosities to consistently atomize and spray the paint in a desired homogeneous pattern.